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US engineers are developing the next-generation of firefighting equipment specially designed to work in space.

An onboard fire is regarded as one of the most frightening hazards for a space mission.

In 1997, astronauts and cosmonauts got firsthand experience when a faulty oxygen candle on board Russia's Mir space station exploded in flames, filling the outpost with thick smoke and blocking half the crew from reaching their lifeboat.

"I did not expect smoke to spread so quickly," says NASA astronaut Jerry Linenger, who was aboard Mir as part of a US-Russian astronaut exchange program.

"(It) was about 10 times faster than I would expect a fire to spread on a space station."

NASA hopes any future space fires will be safely contained in experiment boxes. But it isn't counting on that.

With a new spaceship under development, the agency is investing in next-generation fire-fighting gear that is specially designed to work in microgravity.

"In space, fires are like spheres. They're not shaped like what we have on earth," says James Butz, vice president of operations for ADA Technologies.

Last week the company announced it had received a grant from NASA to continue work on an extinguisher that coats fires in a fine mist.

No escape

The technology is one of two NASA is exploring for use aboard its Orion spacecraft, the follow-on program to the space shuttle. The agency plans to retire the shuttle fleet in 2010 and develop capsule-style ships that can travel to and from the moon.

"There are mainly three emergencies that we train for - a fire, a depressurisation, or if the atmosphere becomes not livable," says Sandra Magnus, who returned last week from a four-month stay on the International Space Station.

"If the situation can't be contained, we basically train to evacuate."

Astronauts aboard Orion will not have that luxury.

Like a fog

ADA's technology would coat a flame in tiny droplets of mist, much like fog, says Butz.

The key to getting the droplets small enough is to use compressed gas. The system uses water and nitrogen so it is non-toxic and has an unlimited shelf life.

Because oxygen and nitrogen will be aboard the spacecraft, the extinguisher can be refilled if needed.

The technology, which has been under development for about a decade, caught NASA's eye about two and a half years ago.

The company's most recent grant is intended to tweak the nozzle design to address issues raised by the surface tension of water droplets.

The other fire-fighting technology under development is water-based foam, which Butz says works well, but is messy in microgravity.